Paul,
I don't think anyone answered your question and with good reason.
This topic is the source of endless debate and those in the know don't
want to go through it again. Check the archives. There is no
agreement as to what the limits are in terms of X number of forwarding
entries or BGP paths, or routes changes per unit of time, but those
are the factors. The limits themselves differ among router vendors
and individual products and even software builds.
The traffic scaling issues are related to routing scaling. The
performance of most routers (all that I know of) is affected by the
routing load, if nothing else because forwarding entries must be
changed somehow. I don't want to comment on this further.
I can't comment on how routers will change. It safe to say the limits
of available technology (routers you can pick from the glossy and
actually buy) will be raised in 1996, though deployment of the latest
technology will proceed at different rates in parts of the Internet
and growth will continue. Administrative efforts such as those to
better aggregate must also continue.
Curtis